After I submitted some levels to the Substance project, Viper more or less said that he pretty much abandoned it, and that I could take over the development if I wanted to.
I wanted to stick to some of the basics of the project: 30+25, not DOOM style (read one of Viper's later posts in the original thread when he decided to not do DOOM style). Some changes will include a slightly steeper difficulty curve, as well as the introduction of a new system at the end.
Edit: Boosted secret level count to 5.

Every six levels will have one secret level (1/5) with one teleporter (though not necessarily on the sixth level). You can blend the themes of the systems, however you should stick to one system's theme. Add a secret entrance if you want, however it may be changed to an extra life secret. Likewise I may add a secret exit. (I'll only tweak secret exits if I get multiple levels from each 6 that has a secret exit or the secret level doesn't match the theme of the parent level.) Just because there are only a few levels per system doesn't mean that I won't accept new levels to a full system. If the new level is better, I'll replace the worst one with it.